A prior art chuck includes a chuck body that can be mounted to a machine for rotating the chuck about an axis. The chuck includes a plurality of master jaws that are mounted in the chuck body for movement in radial directions relative to the rotational axis, Top jaws are mounted to the front faces of the respective master jaws for holding a tool or workpiece during rotation. The top jaws are selected in accordance with size, shape and other characteristics of the tool or workpiece to be gripped,
The front face of the prior art master jaw and the rear face of the prior art top jaw are appropriately configured to enable their interengagement, For example, some prior art top jaws include a plurality of bolt holes which are registrable with a corresponding plurality of threaded bolt holes in the prior art master jaw. Bolts are passed through the top jaw and are threadedly engaged in the corresponding bolt hole of the master jaw to hold the prior art top jaw on the associated prior art master jaw.
Some prior art jaw assemblies also include interengageable members to facilitate the initial alignment of the bolt holes of the top jaw with the threaded bolt holes of the master jaw. For example, some prior art master jaws include forwardly projecting cylindrical dowel pins that are parallel to but spaced from the bolt holes. The rear face of the corresponding prior art top jaw includes cylindrical recesses for receiving the dowel pins. The bolt holes of these prior art jaws are intended to be aligned when the cylindrical dowel pins and the cylindrical recesses are engaged. Other prior art master jaws include a rectangular tongue which is engageable in a correspondingly configured groove on a top jaw for aligning the bolt holes.
Just-in-time (JIT) manufacturing is preferred by many companies to keep their inventory low. Runs of machined parts tend to be smaller with the JIT manufacturing. Thus, a chuck operator could run as few as ten workpieces before switching over to another workpiece. Each run of workpieces is likely to require a new set of top jaws.
The prior art chuck assembly usually does not repeat precisely and accurately once the top jaws are changed. These problems with repeatability are at least partly due to the difficulty of achieving and maintaining precision between the engaged cylindrical or rectangular prior art master jaw/top jaw mounting structures. Even a high degree of precision requires some play to enable the cylindrical or rectangular structures to slidingly mate. As a result, the chuck operator must grind the jaws or go through other alignment procedures to re-attain the specified precision. The time that is lost to periodically regrind the prior art jaws is reflected in the cost of the finished product.
Cycle time also is increased by the constant changing and remachining of the top jaws. Cycle time is the time required to produce a product in the factory from the receipt of the order to shipment. Reducing cycle time is a major competitive strategy. It makes it possible to provide fast response to narrow market windows; reduce work in process (WIP) inventory; produce more in the same factory floor space; improve market forecasts; and provide shorter delivery intervals with improved assurance.
Cycle time could be reduced and the potential efficiencies of JIT manufacturing processes could be achieved by providing master jaws and top jaws that can be changed with no need for remachining or realignment.
In view of the above, it is an object of the subject invention to provide an improved top jaw-master jaw assembly for a chuck.
It is another object of the subject invention to provide a top jaw-master jaw assembly which maintains specified precision after changing top jaws.
Another object of the subject invention is to provide a top jaw-master jaw assembly which reduces set-up time (downtime) and decreases cycle time.